This invention relates generally to the art of gas generation and more particularly to compositions and methods for generating hydrogen gas.
There are currently only a limited number of methods available to produce hydrogen on a small scale. For example, hydrogen gas is generated by the reaction of metals or metal hydrides with acids, bases, water alcohols, etc. Hydrogen gas can also be stored in and released from pressurized gas cylinders. However, these methods are not applicable when severe weight and/or volume restrictions are imposed on a system which must generate relatively small amounts of hydrogen gas (up to about 250 liters) in a short time (less than one minute). The following example will illustrate this point: the reaction LiH + H.sub.2 O .fwdarw. LiOH+H.sub.2 liberates about 27 kcal/mole hydrogen. Assuming 100 percent completion of the reaction within 30 seconds without an available external heat sink, then well over 300 grams of water would be needed to produce 1 mole of hydrogen gas (i.e., 18 grams of water as reactant and the remainder for a heat sink) in order to prevent boiling of the water and the formation of a hydrogen-steam mixture. This means that the weight/volume ratio (reactants (grams) per liter of hydrogen generated) is greater than 14 grams per liter.
Another reaction which has been proposed to generate hydrogen is based on the thermal decomposition of hydrazine bisborane. This reaction is represented by the following equation: EQU N.sub.2 H.sub.4 (BH.sub.3).sub.2 .fwdarw..sup.heat 2NB + 5H.sub.2.
Although in theory this reaction is very favorable in terms of hydrogen produced per gram of reactant (weight - volume ratio is 0.54 grams per liter assuming 100 percent yield), the temperture required to keep the reaction going is high enough to melt glass fiber cloth and the hydrogen produced is at its ignition temperature. In addition, hydrazine bisborane is not commercially available and it is difficult to handle because of its instability.